With the progress of IT and network technology supported by digitalization, an amount of information processed by a person and an electronic device and stored is steadily increasing. Correct data on a phenomenon is acquired by a sensor that is an input device, correctly analyzed, assessed, processed, and recognized as useful information by a person. This is positioned as important activities for constructing a secure and safe society to a human society which becomes unconnected to a large amount of information.
In a modern life, facilities such as a water supply and sewerage network, a high-pressure chemical pipeline for gas, petroleum, or the like, a high-speed railway, a long span bridge, a tower building, a large commercial airplane, a car, and the like are created and used as the infrastructure of an affluent society. If these facilities are broken by natural disaster such as an unexpected earthquake or the like or aged deterioration and this results in a major accident, the accident has a lot of influence on the society and an economic loss is large. Deterioration due to corrosion, abrasion, backlash, or the like of a member used for the facility increases with the time. Lastly, malfunction such as breaking or the like occurs. In order to secure the safety and security of the facilities, many efforts are focused on the technical development beyond the academic areas of science, engineering, social science, and the like. A non-destructive testing technology in which a test can be performed at low cost and by a simple operation becomes important to prevent the major accident due to deterioration and breaking of the facilities.
By the way, as a liquid leakage test performed to detect liquid leakage due to deterioration or breaking of a pipe, a check by ear in which a person hears the sound generated by the leakage is usually used.
However, in many cases, the pipe is buried in the ground or installed on a high place of a building. Therefore, it is dangerous to perform the check by ear and requires a lot of labor. For this reason, the check cannot be performed with high accuracy and cannot be sufficiently performed. Further, a degree of proficiency of a checker has an influence on the accuracy of the result. Currently, because the degree of proficiency of the checker is low, it is difficult to prevent a leakage accident.
Further, when water leak is detected, it is required to specify the location of the leakage with a high degree of accuracy to reduce a repair cost. Today, a specialized checker specifies the location by the check by ear.
However, when an external noise such as a traffic noise generated by traffic or the like exists and a frequency component of the sound generated by the water leak is similar to that of the external noise, the check is disturbed by the external noise and it becomes difficult to determine whether the water leak occurs. For this reason, some countermeasures are taken, for example, the check is performed in a midnight time zone in which the external noise hardly occurs. However, the checker is greatly burdened by this.
In order to solve such problem, various leakage check methods using an instrument are proposed.
Patent Literature 1 (PTL1) discloses a leakage detection device composed of a vibration detection device having a pickup including a piezoelectric element, a detection device main body including a voltage amplifier which performs voltage amplification of an output signal and a plurality of kinds of noise elimination means which eliminate noise from the output signal, and a headphone.
Patent Literature 2 (PTL2) discloses a leak amount measuring device including a video observation device which observes a video of a leaking fluid, a sound measuring device which measures sound of the leaking fluid, a feature amount extraction device which extracts a feature amount of the leaking fluid from the outputs of the video observation device and the sound measuring device, and a leak amount retrieval device which calculates a leak amount by retrieving a database related to the leak amount that is created for each of pressure and temperature of the fluid, a phase state, and an area, a shape, or the like of a leak part.
Patent Literature 3 (PTL3) discloses a water leak detection method of which a water pipe and water in this water pipe are excited by a sound wave emitted by a sound wave source installed to a branch pipe laid on the ground that is connected to a water pipe buried in the ground, the sound wave is detected by a sound wave receiver on the surface of the ground, a signal processing of the detection signal of the sound wave is performed in synchronization with an excitation signal of the sound wave source, and water leak is detected based on a phenomenon in which the level of the detection signal changes according to the presence or absence of water leak.